Cross-linked anionic and amphoteric, organic polymeric compositions are known to those skilled in the art and are useful in a variety of solid-liquid separation applications, particularly in the flocculation of various dispersions of suspended solids, such as sewage sludge, and in the thickening of cellulosic paper pulp suspensions. Modern concerns about environmental pollution and the increasing cost of materials have made it highly desirable to produce flocculating agents which cause higher degrees of separation at lower dosage levels.
EP 0,202,780 describes the preparation of polymeric, crosslinked, cationic acrylamide polymer beads by conventional inverse emulsion polymerization techniques. Crosslinking is accomplished by the incorporation of a difunctional monomer, such as methylenebisacrylamide, into the polymer. This crosslinking technology is well known in the art. The patentee teaches that the crosslinked beads are useful as flocculants.
Typically, the particle size of polymers prepared by conventional inverse water-in-oil emulsion polymerization processes are limited to a range of about 1-5 microns, since no particular advantage in reducing the particle size has hitherto been apparent. The precise particle size which is achievable in inverse emulsions is determined by the concentration and activity of the surfactant(s) employed and these are customarily chosen on the basis of emulsion stability and economic factors.
Leong, et al., in Inverse Microemulsion Polymerization, J. of Phys. Chem., Vol. 86, No. 23, Jun. 24, 1982, pp 2271-3, discloses polymerization of acrylamide in an inverse microemulsion. The author, also discloses having prepared crosslinked polyacrylamide latices or microgels by using a 100:1 mixture of acrylamide-methylenebisacrylamide. No anionic or amphoteric monomers are mentioned or is their use as a flocculating agent or paper-making additive.
EPO 0173605 teaches the production of microbeads having a diameter ranging from about 49-87 nm and produced from terpolymers of vinyl acetate (84.6), ethyl acrylate (65.4) and acrylic acid (4.5) or methacrylonitrile (85), butyl acrylate (65) and acrylic acid (3). These polymeric beads are disclosed as added to an LBKP pulp slurry in order to evaluate the resultant paper for sizing degree, paper force enhancement and disintegratability. These polymer beads fall outside the scope of those claimed in the present invention in that the ionic content thereof is too small to impart any appreciable improvement during usage.
Additionally, U.S. Pat. No. 4,681,912 discloses the production of microparticles of acrylamide and acrylic acid, for example, utilizing a microemulsion process. The patent, however, fails to teach the cross-linking of the particles so as to render them water-insoluble or their use in paper-making.